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The most popular melting furnace in the ferrous foundries is cupola furnace.
Cupola is similar to the blast furnace. It is shaft-like vertical furnace consisting of a steel shell lined with refractory bricks, equipped with tuyeres (nozzles for blowing air).
The liquid iron is periodically (or continuously) removed through a spout.
Iron, coke and limestone flux are charged by means of an opening locating in the upper half of the steel shell.
Ferrous foundries also use arc furnaces for melting iron and steel.
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The Electric Arc Furnace (EAF) uses three vertical carbon rods as electrodes for producing arcs, striking on to the charge and heating it to the required temperature.
Induction furnaces are widely used for melting non-ferrous and ferrous alloys.
There are two types of induction furnaces: coreless induction furnaces and channel induction furnaces:
Coreless induction furnace consists of: a water cooled helical coil made of a copper tube, a crucible installed within the coil and supporting shell equipped with trunnions on which the furnace may tilt.
Alternating current passing through the coil induces alternating currents in the metal charge loaded to the crucible. These induced currents heat the charge.
When the charge is molten, electromagnetic field produced by the coil interacts with the electromagnetic field produced by the induced current. The resulted force causes stirring effect helping homogenizing the melt composition and the temperature.
The frequency of the alternating current used in induction furnaces may vary from the line frequency (50Hz or 60Hz) to high frequency 10,000Hz
Channel type induction furnace consists of a steel shell lined with refractory materials and an inductor attached to the shell. There is a channel connecting the main body with the inductor.
The inductor of the channel furnace works as a transformer. It has a ring-like iron core with a water- or air-cooled coil as a primary coil and a loop of the melt, circulating in the channel, as a secondary coil. Melt circulation has a stirring effect.
Channel induction furnaces work at line frequency currents.
Channel induction furnaces are commonly used as holding furnaces (furnace for maintaining a molten metal, poured from a melting furnace, at a proper temperature).
Channel furnaces are also used for melting low melting point alloys and iron. For two or three shift operation channel furnaces are more economical than coreless furnaces.
Channel furnaces of ratings up to the 10’s of MW and up to capacities of thousands of tonnes have been used for melting and superheating iron.
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Crucible furnaces are used for melting and holding small batches of non-ferrous alloys.
Crucible furnaces are the oldest type of melting furnaces. A refractory crucible filled with the metal is heated through the crucible wall.
There are two main types of crucible furnace:
In the gas fired furnaces heat is provided by a burner directed to the crucible.
In the resistance furnaces electric heating elements are used as a source of heat.
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